Laser-based treatment of tissue is used for a variety of applications, such as hair removal, skin rejuvenation, wrinkle treatment, acne treatment, treatment of vascular lesions (e.g., spider veins, diffuse redness, etc.), treatment of cellulite, treatment of pigmented legions (e.g., age spots, sun spots, moles, etc.), tattoo removal, and various other treatments. Such treatments generally include delivering laser radiation to an area of tissue on a person's body, e.g., the skin or internal tissue, to treat the tissue in a photochemical, photobiological, thermal, or, other manner, which can be ablative or non-ablative, among other properties, depending on the particular application.
Laser-based treatment devices may include any suitable type of laser, e.g., laser diode, fiber laser, VCSEL (Vertical Cavity Surface Emitting Laser), LED, etc. A device may include a single laser or multiple lasers, e.g., a laser diode bar including multiple distinct emitters arranged in a row, or multiple fiber lasers arranged in a row or array.
Diode lasers are particularly suitable for certain treatments and devices for providing such treatments. For example, diode lasers are compact, as they are typically built on one chip that contains all necessary components. Further, diode lasers typically provide an efficiency of up to 50%, which enables them to be driven by low electrical power compared to certain other lasers. Further, diode lasers allow direct excitation with small electric currents, such that conventional transistor based circuits can be used to power the laser.
Other characteristics of diode lasers include high temperature sensitivity/tunability, and a highly divergent beam compared to certain other lasers. Diode lasers typically emit a beam having an axis-asymmetric profile in a plane transverse to the optical axis of the laser. In particular, the emitted beam diverges significantly faster in a first axis (referred to as the “fast axis”) than in an orthogonal second axis (referred to as the “slow axis”). In contrast, other types of lasers, e.g., fiber lasers, typically emit a beam having an axis-symmetric profile in the transverse plane.
Laser-baser treatment devices include larger-scale devices typically operated by a physician or other professional in a clinic or other office, as well as hand-held devices for home-use, allowing users to provide treatment to themselves. Some hand-held laser-baser treatment devices are battery powered, e.g., using a Li ion battery cell (or multiple cells). Such battery-powered devices may be recharged between use, e.g., by plugging into an A/C wall outlet, either directly or by docking in a docking unit plugged into the wall.
Some laser-baser treatment devices apply laser radiation directly from the laser source to the target tissue to create a pattern of radiated areas (e.g., spots, lines, or other shapes) in the tissue. Others include optics between the laser source and the target tissue. Such optics may include optical elements such as lenses, mirrors, and other reflective and/or transmissive elements, for controlling optical parameters of the beam, such as the direction, shape (e.g., convergent, divergent, collimated), spot size, angular distribution, temporal and spatial coherence, and/or intensity profile of the beam. Some devices include systems for scanning a laser beam in order to create a pattern of radiated areas (e.g., spots, lines, or other shapes) in the tissue. For some applications, the scanned pattern of radiated areas overlap each other, or substantially abut each other, or are continuous, in order to provide generally complete coverage of a target area of tissue. For other applications, e.g., certain wrinkle treatments and other skin rejuvenation treatments, the scanned radiated areas may be spaced apart from each other such that only a fraction of the overall target area of the tissue is radiated. In this case, there are generally regions of untreated tissue between regions of treated tissue. This latter type of treatment is known as “fractional” treatment (or more specifically, fractional photothermolysis) because only a fraction of the target area is irradiated.
Laser-baser treatment devices may deliver radiation as continuous wave (CW) radiation, manually pulsed radiation, automatically pulsed radiation, or in any other manner, and according to any suitable parameters, e.g., wavelength, current, power level, etc. For example, a wavelength of about 650 nm to about 1100 nm (e.g., about 810 in some applications) may be used for hair removal treatment. As another example, wavelengths absorbed by water in the skin, e.g., between 1400 nm and 2000 nm, may be used for certain treatments. For certain “fractional” skin treatments, a wavelength of about 1450-1550 nm±50 nm may be used, with a total energy of about 2 mJ-30 mJ delivered to the target tissue at each treatment zone, or “microthermal zone” (MTZ).